The present invention relates to providing wireless (radio) point-to-multipoint services, such as multimedia broadcast and multicast service (MBMS), in UMTS (Universal Mobile Telecommunications System), which is a European type IMT-2000 system, and in particular, to receiving error-free radio MBMS service by a terminal by having the UTRAN re-transmit any portions of data that was received with errors by the terminal.
A universal mobile telecommunication system (UMTS) is a third generation mobile communications system that has evolved from the European Global System for Mobile communications (GSM) that aims to provide an improved mobile communications service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
FIG. 1 illustrates an exemplary basic structure of a UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal 100 (or user equipment: UE), a UTRAN 120, and a core network (CN) 130. The UTRAN 120 includes one or more radio network sub-systems (RNS) 125. Each RNS 125 includes a radio network controller (RNC) 123, and a plurality of Node-Bs (base stations) 121 managed by the RNC 123. The RNC 123 handles the assigning and managing of radio resources, and operates as an access point with respect to the core network 130. The Node-Bs 121 receive information sent by the physical layer of the terminal 100 through an uplink, and transmit data to the terminal through a downlink. The Node-Bs 121, thus, operate as access points of the UTRAN 120 for the terminal 100. Also, the RNC 123 allocates and manages radio resources and operates as an access point with the core network 130.
The service provided to a particular terminal 100 is divided into circuit switched (circuit exchanged) service and packet switched (packet exchanged) service. For example, typical voice telephone service falls under circuit switched (CS) service, while web-browsing service via an Internet connection is classified as packet switched (PS) service. To support circuit switched service, the RNC 123 connects with the MSC 131 of the core network 130, and the MSC 131 connects with the GMSC 133 that manages connections coming from or going out to other networks. For packet switched service, the SGSN 135 and the GGSN 137 of the core network 130 provide appropriate services. For example, the SGSN 135 supports the packet communication going to the RNC 123, and the GGSN 137 manages the connection to other packet switched networks, such as an Internet network.
Between various network structure elements, there exists an interface that allows data to be exchanged for communication therebetween. The interface between the RNC 123 and the core network 130 is defined as the Iu interface. The Iu interface is referred to as “Iu-PS” if connected with the packet switched domain, and referred to as “Iu-CS” if connected with the circuit switched domain. Also, the interface between RNCs is referred to as “Iur” and the interface between an RNC 123 and a Node B 121 is referred to as “Iub”.
FIG. 2 illustrates a radio interface protocol architecture (structure) between the terminal 100 and UTRAN 110 that is based upon 3GPP wireless access network technology. Here, the radio access interface protocol has horizontal layers including a physical layer, a data link layer and a network layer, and has vertical planes including a user plane for transmitting data information and a control plane for transmitting control signals. The user plane is a region to which traffic information of a user, such as voice data or Internet-protocol (IP) packets are transmitted. The control plane is a region to which control information, such as an interface of a network or maintenance and management of a call, is transmitted. In FIG. 2, protocol layers can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well-known in the art of wireless (mobile) communication systems.
Each layer shown in FIG. 2 will now be described. The first layer (L1) uses various radio transmission techniques to provide information transfer service to the upper layers. The first layer (L1) is connected via a transport channel to a medium access control (MAC) layer located at a higher level, and the data between the MAC layer and the physical layer is transferred via this transfer channel.
The MAC layer handles the mapping between the logical channels and the transport channels, and provides a re-allocation service of the MAC parameter for allocation and re-allocation of radio (wireless) resources. The MAC layer is connected to an upper layer called a radio link control (RLC) layer through a logical channel, and various logical channels are provided according to the type of transmitted information. In general, when information of the control plane is transmitted, a control channel is used. When information of the user plane is transmitted, a traffic channel is used. Also, the logical channels include a common channel and a dedicated channel depending on whether the logical channel is shared. The logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH) that provides information including information usable for the terminal to access a system, and a paging control channel (PCCH) used by the UTRAN to access a terminal.
The MAC layer is connected to the physical layer by the transport channel, and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, and a MAC-hs sub-layer according to the type of transport channel to be managed. The MAC-b sub-layer manages a BCH (Broadcast Channel), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH), a downlink shared channel (DSCH) or a paging channel (PCH), which is shared by a plurality of terminals. The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal.
The RLC layer supports reliable data transmissions, and performs a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner upon considering processing capacity, and then creates certain data units with header information added thereto. The created data units are called protocol data units (PDUs), which are then transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
A broadcast/multicast control (BMC) layer performs the functions of scheduling a cell broadcast (CB) message transferred from the core network 200 and of broadcasting the CB message to UEs located in a specific cell or cells. At the UTRAN 100, the CB message transferred from the upper layer is combined with information, such as a message ID, a serial number, a coding scheme, etc., and transferred to the RLC layer in the form of a BMC message and to the MAC layer through a common traffic channel (CTCH), which is a logical channel. The logical channel CTCH is mapped to a transport channel (i.e., a forward access channel (FACH)), and to a physical channel (i.e., a secondary common control physical channel (S-CCPCH).
A packet data convergence protocol (PDCP) layer is located at an upper layer from the RLC layer, allowing data to be transmitted effectively via a radio interface with a relatively small bandwidth through a network protocol, such as the IPv4 or the IPv6. For this purpose, the PDCP layer performs the function of reducing unnecessary control information used in a wired network, and this function is called, header compression. Various types of header compression techniques, such as RFC2507 and RFC3095 (robust header compression: ROHC), which are defined by an Internet group called the IETF (Internet Engineering Task Force), can be used. These methods allow transmission of only the absolutely necessary information required in the header part of a data, and thus transmitting a smaller amount of control information can reduce the overall amount of data to be transmitted.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane, and controls the transport channels and the physical channels in relation to the establishing, the re-establishing, and the releasing of the radio bearers (RBs). Here, the RB signifies a service provided by the second layer (L2) for data transmission between the terminal 10 and the UTRAN 100. In general, the establishing of the RB refers to the setting of the characteristics of the radio protocol layers and channels for providing a particular service, and also refers to the procedures in setting the individual particular parameters and operation methods.
Among the RBs, the particular RB used between the UE and the UTRAN for exchanging RRC messages or NAS messages is called a SRB (Signaling Radio Bearer). When an SRB is established between a particular UE and the UTRAN, a RRC connection exists between the UE and the UTRAN. A UE having a RRC connection is said to be in RRC connected mode, and a UE without a RRC connection is said to be in idle mode. When a UE is in RRC connected mode, the RNC determines the cell in which the UE is located (i.e., the RNC determines the UE location in units of cells), and manages that UE. For a UE in RRC connected mode, signaling messages can be sent to the UTRAN. The UE having RRC connection remains in one state, among the states of CELL_DCH, CELL_PCH, URA_PCH, or CELL_FACH, according to the instructions of the UTRAN.
In CELL_DCH state, the UE is allocated a dedicated physical channel, and uses a dedicated traffic channel and a dedicated control channel. In CELL_FACH state, the UE is allocated a dedicated control channel, and is additionally allocated a dedicated traffic channel. In CELL_PCH state and in URA_PCH state, the UE does not have a dedicated traffic channel or a dedicated logical channel established with the UTRAN. In CELL_FACH state and in CELL_DCH state, the UE can always send and receive messages with the UTRAN because a dedicated control channel exists. However, in URA_PCH state or in CELL_PCH state, when the UE has a message that needs to be sent to the UTRAN, the UE changes to the CELL_FACH state upon performing a cell update procedure and then is able to exchange messages with the UTRAN.
Next, multimedia broadcast/multicast service (MBMS) will be described. MBMS refers to a downlink transmission service for providing data services such as, streaming services (e.g., multimedia, video on demand, webcast) or background services (e.g., e-mail, short message services (SMS), downloading), to a plurality of terminals by employing a downlink dedicated MBMS bearer service. At the UTRAN, for the MBMS bearer, a point-to-multipoint (p-t-m) radio bearer and a point-to-point (p-t-p) radio bearer services are used.
MBMS can be classified into a broadcast mode and a multicast mode. The MBMS broadcast mode refers to transmitting multimedia data to all users within a broadcast area, which is a region where broadcast service is possible. In contrast, MBMS multicast mode refers to transmitting multimedia data to only a certain specified user group within a multicast area, whereby a multicast area, which is a region where multicast service is possible.
FIG. 3 shows a process in which a UMTS network provides a particular MBMS service (service 1) by using multicast mode. Also, FIG. 3 depicts an example when the UEs (UE1 and UE2) receive a particular service (service 1). First, the users (UE1 and UE2) desiring to receive a MBMS service must perform a subscription procedure. Here, subscription refers to the acts of establishing a relationship between the service provider and the user.
Also, users (UEs) wishing to receive an MBMS service must also receive a service announcement provided from the network. Here, service announcement refers to the function of informing the terminal about a list (index) of the services to be provided and related information. Also, if the user (UE) intends to receive a multicast mode MBMS service, the user (UE) should join a multicast subscription group. Here, ‘multicast group’ refers to a group of users that receive a specific multicast service, and ‘joining’ means merging with the multicast group that has particular users who wish to receive the specific multicast service. Using this joining procedure, the terminal can inform the UTRAN of its intent to receive the particular multicast data (multicast service). In contrast, for a terminal that has joined a particular multicast group, the procedure for terminating the joining of the multicast group is referred to as ‘leaving’. The above-described subscribing, joining, and leaving procedures are performed for each terminal, and a terminal may perform the subscribing, joining, and leaving procedures before, during, or any time after data transmission.
While a particular MBMS service is in progress, one or more sessions for that service may occur in sequence. Here, a session may be defined in various ways. For example, a session may be each complete episode of a multi-episode drama or a session may be certain portions of a sports program, such as scenes that show goals in a soccer match. When data to be transmitted for a particular MBMS service is generated at the MBMS data source, the core network (CN) 130 informs a session start to the RNC 123. In contrast, when there is no further data at the MBMS data source to be transmitted for a particular MBMS service, the core network (CN) 130 informs a session stop to the RNC 123. Between the session start and the session stop, a data transfer procedure for the particular MBMS service can be performed. Here, only those terminals that have joined a multicast group for the MBMS service may receive data that is transmitted by the data transfer procedure.
In the above session start procedure, the UTRAN that received the session start from the core network (CN) transmits an MBMS notification to the terminals. Here, MBMS notification refers a function of the UTRAN for informing a terminal that the transmission of data for a particular MBMS service within a certain cell is impending. The UTRAN can use the MBMS notification procedure to perform a counting operation that determines the number of terminals that wish to receive a particular MBMS service within a particular cell. The counting procedure is used to determine whether the radio bearer for providing the particular MBMS service should be set as point-to-multipoint (p-t-m) or point-to-point (p-t-p). For selecting the MBMS radio bearer, the UTRAN internally establishes a threshold value. After performing the counting function, the UTRAN may set a point-to-point MBMS radio bearer if the number of terminals existing within the corresponding cell is smaller than the threshold value, and may set a point-to-multipoint MBMS radio bearer if the number of terminals existing within the corresponding cell is greater than or equal to the threshold value.
If a point-to-point radio bearer is to be set, the UTRAN allocates a dedicated logical channel to each terminal (UE) and sends the data of the corresponding service. If a point-to-multipoint radio bearer is to be set, the UTRAN uses a downlink common logical channel to send the data of the corresponding service.
When the system provides a particular MBMS service to the terminals (UEs) by establishing a point-to-point radio bearer, because the system is in one-to-one connection with each terminal, the system may (if necessary) receive feedback from each terminal, and use the information about which data blocks the terminal received and which data blocks the terminal did not receive, or the error rate of the data such that any necessary data blocks may be re-transmitted to the terminal. However, when a point-to-multipoint radio bearer is established, a plurality of terminals use this radio bearer, thus the system cannot receive feedback of each terminal to re-transmit data or compensate for data errors according to the reception state of each terminal. Accordingly, when the UTRAN uses a point-to-multipoint radio bearer to provide MBMS service, there will be certain terminals that could not receive data or that receive data with errors therein. When terminals do not completely receive proper data, service quality is severely degraded, thus causing problems in the conventional art.